Two subvertical gabbroic dikes with widths of ~ 350 m (East-Muren) and ≥ 500 m (West-Muren) crosscut continental flood basalts in the Antarctic extension of the ~ 180 Ma Karoo large igneous province (LIP) in Vestfjella, western Dronning Maud Land. The dikes exhibit unusual geochemical profiles; most significantly, initial (at 180 Ma) ε_Nd values increase from the dike interiors towards the hornfelsed wallrock basalts (from − 15.3 to − 7.8 in East-Muren and more gradually from − 9.0 to − 5.5 in West-Muren). In this study, we utilize models of partial melting and energy-constrained assimilation‒fractional crystallization in deciphering the magmatic evolution of the dikes and their contact aureoles. The modeling indicates that both gabbroic dikes acquired the distinctly negative ε_Nd values recorded by their central parts by varying degrees of assimilation of Archean crust at depth. This first phase of deep contamination was followed by a second event at or close to the emplacement level and is related to the interaction of the magmas with the wallrock basalts. These basalts belong to a distinct Karoo LIP magma type having initial ε_Nd from − 2.1 to + 2.5, which provides a stark contrast to the ε_Nd composition of the dike parental magmas (− 15.3 for East-Muren, − 9.0 for West-Muren) previously contaminated by Archean crust. For East-Muren, the distal hornfelses represent partially melted wallrock basalts and the proximal contact zones represent hybrids of such residues with differentiated melts from the intrusion; the magmas that were contaminated by the partial melts of the wallrock basalts were likely transported away from the currently exposed parts of the conduit before the magma–wallrock contact was sealed and further assimilation prevented. In contrast, for West-Muren, the assimilation of the wallrock basalt partial melts is recorded by the gradually increasing ε_Nd of the presently exposed gabbroic rocks towards the roof contact with the basalts. Our study shows that primitive LIP magmas release enough sensible and latent heat to partially melt and potentially assimilate wallrocks in multiple stages. This type of multi-stage assimilation is difficult to detect in general, especially if the associated wallrocks show broad compositional similarity with the intruding magmas. Notably, trace element and isotopic heterogeneity in LIP magmas can be homogenized by such processes (basaltic cannibalism). If similar processes work at larger scales, they may affect the geochemical evolution of the crust and influence the generation of, for example, massif-type anorthosites and “ghost plagioclase” geochemical signature.

在西德伦宁莫德的韦斯特菲拉~~ 180 Ma Karoo大火成岩省（LIP）的南极延伸中，两个宽约350 m（东穆伦）和≥500 m（西穆伦）的横断面三角洲堤坝横切了大陆性洪泛玄武岩。土地。堤防表现出不同寻常的地球化学特征。最显着的是，初始_Nd值（在180 Ma处）从堤防内部向角els壁岩玄武岩增加（东穆伦从-15.3增至-7.8，西穆伦从-9.0增至-5.5）。在这项研究中，我们利用部分熔融和能量约束的同化-分形结晶模型来解释堤防及其接触性金极的岩浆演化。建模表示两个辉长岩脉中取得的明显负ε_钕通过深处太古代壳的同化程度不同，通过中心部分记录的数值。在第一阶段的深层污染之后，发生了第二个事件，其发生在或接近就位水平，并且与岩浆与围岩玄武岩的相互作用有关。这些玄武岩属于具有初始ε鲜明卡鲁LIP岩浆型_的Nd从- 2.1至+ 2.5，从而提供了形成鲜明对比的ε_的Nd堤防父母岩浆的组成（东穆伦为− 15.3，西穆伦为9.0），以前曾被太古宙壳污染。对于东穆伦（East-Muren），远方角岩代表部分熔融的围岩玄武岩，近侧接触区代表此类残留物的杂种，其中侵入岩具有不同的熔体。在岩浆与围岩接触被密封并防止进一步同化之前，被围岩玄武岩的部分熔体污染的岩浆很可能从管道的当前裸露部分运走。相反，对于西木人，围岩玄武岩部分熔融的同化由ε逐渐增加记录_的Nd暴露的辉长岩中的一部分朝向与玄武岩接触的屋顶。我们的研究表明，原始的LIP岩浆释放出足够的感性和潜热，从而在多个阶段中部分融化并潜在地吸收了围岩。通常，这种类型的多阶段同化很难检测到，特别是如果相关的围岩与侵入岩浆表现出广泛的成分相似性的话。值得注意的是，LIP岩浆中的痕量元素和同位素异质性可通过此类过程（玄武质食人症）被均化。如果类似的过程在更大的规模上起作用，它们可能会影响地壳的地球化学演化，并影响例如地块型钙长石和“鬼斜长石”地球化学特征的产生。